1. Technical Field of the Invention
The present invention relates to a method for producing cyclohexanone oxime by ammoximation of cyclohexanone. Cyclohexanone oxime is useful as a starting material for producing ε-caprolactam, or the like.
2. Related Art
For producing cyclohexanone oxime, there has been proposed a method of subjecting cyclohexanone to ammoximation with hydrogen peroxide and ammonia in the presence of titanium silicate catalyst (e.g., Japanese Patent Application Laid-Open No. (JP-A-) 62-59256, JP-A-6-49015, JP-A-6-92922, and JP-A-7-100387).
Such a method has advantages in that it does not need to neutralize sulfuric acid with ammonia, while the neutralization is conducted in the conventional method of ammoximation with hydroxylamine sulfate, and in that product separation from the catalyst can be easily carried out since a solid catalyst is utilized.
However, in the above ammoximation reaction, the catalytic activity of the titanium silicate catalyst is gradually deteriorated with the passage of reaction time so that the conversion rate of cyclohexanone and the selectivity to cyclohexanone oxime may become insufficient. As a result, the yield of cyclohexanone oxime tends to be lowered.
In order to maintain a desired yield of cyclohexanone oxime, it is necessary to exchange the catalyst which has been used to some extent to be degraded, with a brand-new catalyst. If such a degradation of the catalyst can be suppressed, the frequency of the catalyst exchange can be reduced, and therefore, the method has advantages in view of catalyst cost.